This invention relates to a saw blade and to a tip therefor and particularly relates to a circular saw blade and a carbide tip having a concave rake face.
Circular saws using blades having carbide tips have been in use for many years and have provided significant advantages over hardened steel blades. For example, it is known that circular saws using blades with carbide tips may be operated at much higher cutting speeds while retaining a cutting sharpness for a relatively longer period. This provides for a much greater operating efficiency with significantly improved results.
However, due to the inherently brittle nature of carbide tips, the rake angle utilized heretofore has been in a range of zero to 20 degrees. In addition, while the rake face may be angled from side to side, the rake face typically has been flat and has provided generally uniform thickness of the tip. With a tip of generally uniform thickness supported and secured in an accommodating notch of tooth of the blade, the tip was thus positioned to be subjected to generally harmless compressive forces during use of the blade. This arrangement avoided, for the most part, the subjecting of the tip to undesirable shearing stresses which have a tendency to break the carbide tip.
Consequently, in order to avoid the potential for breaking carbide tips of a circular saw blade, the rake face has been flat and the rake angle typically has been limited to a range of zero 20 degrees as noted above. While the carbide tip for circular saw blades has brought many significant advantages to the circular saw blade users, the brittless factor heretofore has imposed significant limtations in performance.
In addition, when using a carbide tip formed with a flat rake face, the chips resulting from the cutting of the work piece, tend to flow down the flat or straight surface of the tip. The chips then must exit from the area of the tip by being worked between the body of the saw blade and the work piece. This creates an undesirable interference in the working area of the saw with resultant inefficiencies.
In at least one past teaching, teeth are formed integrally with the blade with each tooth being formed with a generally curved rake face from top to bottom. The curved face provides more rake to the cutting edge. The structure also provides a freer discharge of the debris.
In another past teaching, a carbide tip is used with a chain saw and is formed with a concave cutting face. The tip is formed with slots and a side surface to firmly seat the tip onto a supporting chain link of the saw. The tip straddles and extends considerably from each side of the link. Further, the tip extends a considerable distance from the concave cutting face to the rear of the tip apparently to provide substantial bulk behind the concave surface and thereby avoid breaking of the brittle carbide tip. The tip-supporting link is concave in the area immediately in front of the concave face of the tip.
In the cutting action of the chain saw, the concave face of the tip is fed in a linear direction into engagement with the workpiece whereby the tip is supported firmly by the bulk thereof and the link shoulder. Even though the cutting face of the tip is concave, the linear feed of the tip into the workpiece apparently results in the tip being subjected mainly to harmless compressive forces and few shear forces. By comparison, a circular saw blade is moved in a curvilinear direction into engagement with the workpiece whereby carbide tips are subjected to comparatively greater shear stress forces which have the tendency to break the brittle carbide tips.
Thus, in the circular saw industry, there is a need for a conventionally-mounted carbide tip having a curved or concave rake face profile to obtain the advantages of high rake angles currently not available with conventional state-of-the-art carbide tips used with circular saws.
In typical steel blade manufacture, integrally formed teeth are alternately spring set to produce a kerf width which is greater than the thickness of the body of the blade. This is obviously desirable to prevent any portion of the body of the blade from rubbing against and burning the workpiece and also to maintain the efficient operation of the circular saw.
In one teaching of a circular saw blade employing carbide tips, the teeth which support the tips are spring set alternately in the manner of the steel blade. Apparently, the carbide tips are not sprung in the blade mountings but are alternately moved to one side or the other of the plane of the blade body along with the spring set teeth.
In another teaching, carbide tips are mounted in a conventional manner on the blade body. Thereafter the sidewalls are ground inwardly on both sides from top to bottom. The top surface of the tip may then be bevelled downwardly from the side which includes the cutting point of the tip to the opposite side. The formation of the top bevel cooperates with the ground sides, theoretically to create a retracted non-cutting portion of the tip which is located on the side of the blade common with the cutting portions of the immediately adjacent tips. The retraction is typically about 0.001 inch to 0.002 inch and functions as a side clearance angle. Thus, the grinding of the side angles and the top bevel tends to provide a tip configuration necessary to obtain clearances to preclude the rubbing of non-cutting portions of the tips against the kerf wall of the workpiece and thereby to avoid the resultant deleterious effects.
However, from a practical standpoint, it is difficult to obtain and maintain the necessary parameters in assembling tips to blades and in the successive side and top bevel grinding of the assembled tips. For example, each tip ideally would have to be placed and secured perfectly on the blade in precisely the same relative location as the other tips on the blade. While the positioning of the tip is critical, there is also concern for any subsequent finishing operation, such as by grinding, which could alter the previous accurate positioning of the tip on the blade.
The grinding implements are typically set to angularly grind precise amounts of material from each side and top of the mounted tip assuming that the tip has been properly positioned. If the tip is tilted or set too far to one side of the blade, the subsequent side grinding and top bevelling operations will not accomplish the necessary result. Further, as the grinding implements and the supporting structure therefor become worn or shift in their mountings, the results of subsequent grinding operations are affected and the tips are not finished with the necessary parameters to provide the designed clearances.
Under these conditions, the non-cutting tops and edges of some tips of a given blade will extend laterally beyond the cutting point of at least the preceding tip. This creates a shear width which is wider than the designed shear width where the extended tops and sides actually and undesirably cut into the workpiece. This action also creates a drag in the operation of the blade with attendant inefficiencies.
Thus, there is a need in the circular saw industry for a carbide tip having a profile which will provide the necessary retraction clearance for obtaining the designed kerf width in an efficient manner. Further, there is a need for a carbide tip profile which will accommodate tolerances required in normal high speed production methods employed in the manufacture of circular saw blades.
In summary, the current state-of-the-art carbide tips used with circular saw blades present a myriad of problems and limitations as noted above. Ideally, these problems and limitations could be minimized by a single carbide tip having a profile which would provide relatively larger rake angles and adequate side clearance. Therefore, in addition to the need for a variety of designs of carbide tips to overcome each of the different problems and limitations noted above, there is also a need for a single design of a carbide tip which has a profile for overcoming all of the above-noted problems and limitations.